Method to selectively identify reliability risk die based on characteristics of local regions on the wafer

ABSTRACT

A method and system for selectively identifying reliability risk die based on characteristics of local regions on a wafer by computing particle sensitive yield and using the particle sensitive yield to identify reliability risk die. Specifically, a bin characteristics database which identifies hard and soft bins that are sensitive to different failure mechanisms is maintained, and the bin characteristics database is used to compute particle sensitive yield. It is determined whether the particle sensitive yield of the local region around the current die is less than a pre-set threshold, and the die is downgraded if the particle sensitive yield of the local region around the current die is less than the pre-set threshold. If the particle sensitive yield of the local region around the current die is not less than the pre-set threshold, the die is not downgraded.

BACKGROUND

[0001] The present invention generally relates to methods and systemsfor identifying reliability risk die on a wafer, and more specificallyrelates to a method and system for selectively identifying reliabilityrisk die based on characteristics of local regions on the wafer.

[0002] Presently, in identifying reliability risk die on a wafer, it istypically assumed that failing die are primarily caused by particle typedefects, that particle type defects occur in localized regions on thewafer, and that test coverage is never 100 percent, so die with actualdefects will still pass wafer sort tests. Hence, good die in bad regionsare likely to be reliability risks.

[0003] A prior art approach at identifying reliability risk die on thewafer is illustrated in FIG. 1. A threshold is pre-set with regard toyield in the local region around the die. If the yield is less than thepre-set threshold, the die is downgraded. On the other hand, if theyield is not less than the pre-set threshold, the die is not downgraded.The problem with the approach is that, contrary to the first assumptionidentified above, not all failing die are due to particle type defects.Hence, the approach illustrated in FIG. 1 typically results in excessivedowngrading.

OBJECTS AND SUMMARY

[0004] An object of an embodiment of the present invention is to providea method and system for identifying reliability risk die based oncharacteristics of local regions on the wafer, which results in a 80-90%reduction in fallout.

[0005] Another object of an embodiment of the present invention is toprovide a method and system for identifying reliability risk die basedon characteristics of local regions on the wafer, which results inbetter resolution of reliability risk die.

[0006] Briefly, and in accordance with at least one of the foregoingobjects, an embodiment of the present invention provides a method andsystem for selectively identifying reliability risk die based oncharacteristics of local regions on a wafer by computing particlesensitive yield and using the particle sensitive yield to identifyreliability risk die. Specifically, a bin characteristics database whichidentifies hard and soft bins that are sensitive to different failuremechanisms is maintained, and the bin characteristics database is usedto compute particle sensitive yield. It is determined whether theparticle sensitive yield of the local region around the current die isless than a pre-set threshold, and the die is downgraded if the particlesensitive yield of the local region around the current die is less thanthe pre-set threshold. If the particle sensitive yield of the localregion around the current die is not less than the pre-set threshold,the die is not downgraded.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007] The organization and manner of the structure and operation of theinvention, together with further objects and advantages thereof, maybest be understood by reference to the following description, taken inconnection with the accompanying drawing, wherein:

[0008]FIG. 1 illustrates a prior art approach at identifying reliabilityrisk die on the wafer;

[0009]FIG. 2 illustrates an approach at selectively identifyingreliability risk die based on characteristics of local regions on awafer, where the approach is in accordance with an embodiment of thepresent invention;

[0010]FIG. 3 illustrates a system which is in accordance with anembodiment of the present invention, and which can be used to performthe method illustrated in FIG. 2; and

[0011]FIG. 4 illustrates the reduction in fallout as a result of usingthe method and system illustrated in FIGS. 2 and 3.

DESCRIPTION

[0012] While the invention may be susceptible to embodiment in differentforms, there is shown in the drawings, and herein will be described indetail, a specific embodiment with the understanding that the presentdisclosure is to be considered an exemplification of the principles ofthe invention, and is not intended to limit the invention to that asillustrated and described herein.

[0013] As shown in FIG. 2, an embodiment of the present inventionprovides a method for selectively identifying reliability risk die basedon characteristics of local regions on a wafer by computing particlesensitive yield and using the particle sensitive yield to identifyreliability risk die. Specifically, a bin characteristics database whichidentifies hard and soft bins that are sensitive to different failuremechanisms (like particles) is maintained, and the bin characteristicsdatabase is used to compute particle sensitive yield. It is determinedwhether the particle sensitive yield of the local region around thecurrent die is less than a pre-set threshold, and the die is downgradedif the particle sensitive yield of the local region around the currentdie is less than the pre-set threshold. If the particle sensitive yieldof the local region around the current die is not less than the pre-setthreshold, the die is not downgraded.

[0014]FIG. 3 illustrates a system which is in accordance with anembodiment of the present invention, and which can be used to performthe method illustrated in FIG. 2. As shown, the system includes a bincharacteristics database which identifies hard and soft bins that aresensitive to different failure mechanisms (like particles), and means,such as code, for using the bin characteristics database to computeparticle sensitive yield. The system also includes means, such as code,for using the particle sensitive yield to identify reliability risk die,and means, such as code, for determining whether the particle sensitiveyield of the local region around the current die is less than a pre-setthreshold. The system includes means, such as code, for downgrading thedie if the particle sensitive yield of the local region around thecurrent die is less than the pre-set threshold, and not downgrading thedie if the particle sensitive yield of the local region around thecurrent die is not less than the pre-set threshold. The system alsoincludes means, such as code, for considering a subsequent die andrepeating the process.

[0015] As shown in FIG. 4, the present invention provides an approach atidentifying reliability risk die based on characteristics of localregions on the wafer, which can result in a 80-90% reduction in fallout.In each of the vertical bar pairs for each lot, the left-most verticalbar corresponds to the prior art approach shown in FIG. 1, and theright-most vertical bar corresponds to the inventive approach shown inFIG. 2. The present invention provides an approach which results inbetter resolution of reliability risk die.

[0016] While an embodiment of the present invention is shown anddescribed, it is envisioned that those skilled in the art may devisevarious modifications of the present invention without departing fromthe spirit and scope of the appended claims.

1. A method to selectively identify reliability risk die based oncharacteristics of local regions on a wafer, said method comprising:computing particle sensitive yield of a local region around a die on thewafer; using the particle sensitive yield to identify whether the diemay be a reliability risk based on the particle sensitive yield whichwas computed; and repeating the process for additional die on the wafer.2. A method as recited in claim 1, further comprising maintaining a bincharacteristics database.
 3. A method as recited in claim 2, wherein thebin characteristics database identifies hard and soft bins that aresensitive to different failure mechanisms.
 4. A method as recited inclaim 3, wherein the bin characteristics database identifies hard andsoft bins that are sensitive to particle type defects.
 5. A method asrecited in claim 1, further comprising using code to compute particlesensitive yield and identify reliability risk die.
 6. A method asrecited in claim 1, further comprising maintaining a bin characteristicsdatabase, and using the bin characteristics database to compute particlesensitive yield.
 7. A method as recited in claim 1, further comprisingdetermining whether the particle sensitive yield of the local regionaround the current die is less than a pre-set threshold.
 8. A method asrecited in claim 7, further comprising downgrading the die if theparticle sensitive yield of the local region around the current die isless than the pre-set threshold.
 9. A method as recited in claim 7,further comprising downgrading the die if the particle sensitive yieldof the local region around the current die is less than the pre-setthreshold, and not downgrading the die if the particle sensitive yieldof the local region around the current die is not less than the pre-setthreshold.
 10. (Cancelled)
 11. A system to selectively identifyreliability risk die based on characteristics of local regions on awafer, said system comprising: means for computing particle sensitiveyield; and means for using the particle sensitive yield to identifyreliability risk die.
 12. A system as recited in claim 11, furthercomprising a bin characteristics database.
 13. A system as recited inclaim 12, wherein the bin characteristics database identifies hard andsoft bins that are sensitive to different failure mechanisms.
 14. Asystem as recited in claim 13, wherein the bin characteristics databaseidentifies hard and soft bins that are sensitive to particle typedefects.
 15. A system as recited in claim 11, wherein the means forcomputing particle sensitive yield comprises code.
 16. A system asrecited in claim 11, further comprising a bin characteristics database,and means for using the bin characteristics database to compute particlesensitive yield.
 17. A system as recited in claim 11, further comprisingmeans for determining whether the particle sensitive yield of the localregion around the current die is less than a pre-set threshold.
 18. Asystem as recited in claim 17, further comprising means for downgradingthe die if the particle sensitive yield of the local region around thecurrent die is less than the pre-set threshold.
 19. A system as recitedin claim 17, further comprising means for downgrading the die if theparticle sensitive yield of the local region around the current die isless than the pre-set threshold, and not downgrading the die if theparticle sensitive yield of the local region around the current die isnot less than the pre-set threshold.
 20. A system as recited in claim19, further comprising means for considering a subsequent die andrepeating the process.